Found this:
“How can I display an image in the same Post or Page without it being a part of the Gallery?
Any image you upload in the same Post or Page where your Gallery appears will automatically be included in that Gallery. Inserting an image which was uploaded via “Media>Add New” in the Dashboard is not attached to a specific Post or Page and will become attached to the Post or Page where your Gallery appears. This causes the image to be displayed twice, once in the Gallery and again indivdually. The solution is to upload the image to your Media Library from a different, existing Post or Page. Once your images have finished uploading, save your changes and then close the Image Uploader, then go back to the Post or Page where you want to insert the separate image. Click on the “Add Image” button and in the Image Uploader, click on “Insert in Post” button to insert the individual image in your Post or Page. In order to avoid navigation problems, you should link the image to either “None” or “Image URL”.” Ref: https://gammagirl.wordpress.com/2008/07/27/not-the-official-wordpresscom-gallery-faq/
Very annoying but it works and I guess I will have to use it. I am thinking of creating one not published page where I will only attach all the images used as headers for the other pages i will create, by doing this those images won’t be attached to each page as I will insert them via the media library resulting not be displayed in the pages gallery.
